Add FIQ glue for ARM64 cpus and register a handler with the secure world (TLK).
TLK handles the FIQ interrupts and calls our handler after it is done saving
the context. We then get the FIQ context via a SMC call and pass it to the
FIQ handler registered by the kernel (using fiq_glue_register_handler).

The FIQ debugger calls fiq_glue_register_handler() to register its handler
which we in turn call whenever a FIQ fires. The glue saves all the registers,
elr/spsr values and SP, which is then used by tlk_fiq_handler() to pass on to
the actual handler.